Document reproduction machines are known in the art which utilize fiber optic linear illuminators to provide a line illumination at a document platen. For xerographic copiers, it is desirable to provide a uniform band of illumination along a scan strip on the document platen. The illumination source or, alternatively, the document, are moved, and a flowing image is projected onto a photoreceptor surface forming a latent image thereon. The uniformly illuminated line can be provided by means of a plurality of optical fibers which have a circular input face but a fan-like output face. A typical formulation is shown in FIG. 1 of U.S. Pat. No. 4,190,347. There, a light source 26 is directed into the input face of a fiber optic bundle 24. The light-emitting ends of the circular fibers are tightly grouped together at a receiving face 30 and the light-emitting ends juxtaposed along a line 32 to form a linear slit 34. The light-emitting face can comprise one or a plurality of layers. A problem with this configuration is that two or more rows of fibers are typically required to provide the required uniformity of the band of illumination exiting the output face. This requirement increases the expense of the illuminator. Because of the large number of fibers and their closely-packed density, the device is prone to unavoidable fiber breakage or splitting in the light emitting end, both factors resulting in non-uniform illumination at the illuminated plane. The solution to this problem in U.S. Pat. No. 4,190,347 was to introduce a cylindrical lens 36 between the light-emitting end face and the document 14.
Other prior art which utilize fiber optic bundles having linear end faces are disclosed in U.S. Pat. Nos. 3,982,829 and 4,597,030. In the former patent a plurality of fiber optics are bundled together to form a circular light receiving input end and a linear light emitting end positioned adjacent a document platen. U.S. Pat. No. 4,597,030 discloses a surgical illuminator which is linear at both end faces.
It is known in the art to utilize linear electronic print bars to generate images at a photoreceptor during the exposure mode. One example is shown in U.S. Pat. No. 4,763,142. Here a linear light source is required to provide a uniform band of illumination into the entrance face of the linear bar. The bar may, for example, comprise a plurality of liquid crystal cells whose transparency is controlled by a voltage input corresponding to image signals from a remote source. Light from the illuminator source is transmitted through the image bar as a modulated output, the modulation depending upon the instant state of the liquid crystal cells. Another example is disclosed in U.S. Pat. No. 4,718,752. Here an electrooptic image bar 12 is illuminated by an illuminator 24 and modulated to produce the desired modulated output at a photosensitive image plane. One problem with these types of prior art systems is that the light source must be linear to match the geometry of the light-bar orifices and must provide high intensity uniform illumination in order that reasonable operating speeds and good print quality can be achieved. Fluorescent tubes have been used for this purpose but output uniformity depends on the distribution of condensed mercury vapor on the bulb, and the phosphors tend to overheat at the higher operating powers, appreciably degrading light output. Linear tungsten filament bulbs have also been used but lamps with long unsupported filaments are prone to vibration and sagging. On the other hand, bulbs with supported or segmented filaments tend to be non-uniform in light output, and heavy self-supporting filaments require very high power input. Laser beam inputs, such as used in the 4,718,752 patent, are relatively costly.
According to the present invention, an optical fiber illuminator is described which provides a uniform line of illumination at either a document platen, for illumination purposes, or at the input face of an image bar. The optical fiber illuminator is formed in a first embodiment using a plurality of relatively course optical fibers. The fibers are configured so as to form a generally circular, light-receiving input face. The end face is formed into a linear shape in which each fiber end is changed, in one embodiment, by a heat and pressure process, from a circular to a generally rectangular configuration. Reforming the fiber ends eliminates the need to use multiple layers of very fine fibers, as required by the prior art devices, to have the finished line source appear continuous. Output intensity is also enhanced because the dead space between close packed round fibers, which is about 10%, is virtually eliminated. In a second embodiment, the overall light collection efficiency for a given lamp geometry is enhanced by reforming the input end of the fiber bundle as well. Using relative few large fibers rather than many small ones makes fabrication much easier and cheaper because the larger fibers are easier to handle and winding a single layer of the courser, larger fibers, is much faster.
More particularly, the present invention is directed towards a linear illuminator comprising a light source and a plurality of optical fibers formed into a light conducting array; the fibers having a light receiving end placed adjacent said light source and a light-transmitting end placed adjacent a linear plane to be uniformly illuminated, the light receiving end of said fibers being circular and being grouped together to form a generally circular array said light-transmitting ends of said fibers being generally rectangular and formed into a linear array.